We will collect electron diffraction and image data used in the determination of the structure of so atomic resolution. High resolution images will be recorded unique combination of instrumentation including our resolution cold stage and spot-scan illumination system, that should give images of superior quality. For determining the three-dimensional structure, images will be recorded from specimens tilted up to 60 degrees, taking advantage of improvements we have made in overcoming problems of specimen flatness. Electron diffraction data will be recorded from specimens which have been labelled with heavy atom complexes at specific amino acids. Difference Fourier techniques will be used to determine the positions of these heavy atoms in the projection density map. This information will be useful in assigning regions of the three-dimensional density map to particular regions of the primary sequence.